text: Having established the composition of Prussian blue, Gadolin suggested a method for precipitating ferrous iron as ferro ferricyanide, preceding the work of Gay-Lussac by forty years.
  Reports of many of Gadolins chemical investigations appeared in German in Crells Chemische Annalen für die Freunde der Naturlehre, Arzneygelahrheit, Haushaltungskeit und Manufacturen.  In 1825 he published Systema fossilium analysibus chemicis examinatorum secundum partium constitutivarum rationes ordinatorium, a system of mineral classification based upon chemical principles. The introduction outlines Gadolin's theories, and the text presents mineral species in a systematic ordering.
  One of Gadolins latest studies was the chemical analysis of the Chinese alloy pak tong' in 1810 and 1827. Also known as alpacca or German silver, it was a less expensive silver substitute often containing copper, zinc, nickel, and tin.
  Gadolin is also famous for publishing one of the earliest examples of counter-current condensers.  In 1791 he improved a condenser design of his father's by using the "counter-current principle". By requiring water coolant to flow uphill, the effectiveness of the condenser was increased. This principle was later used by Justus Liebig, in what is today usually referred to as a Liebig condenser.